This invention generally relates to a multi-beam scanning system with a time sharing beam control and, more particularly, to an image forming apparatus such as a laser printer having a scanning exposure step by a multi-laser beam and a printing step by an electrophotographic process.
Recently, a laser printer having a scanning exposure step by a laser beam and a printing step by an electrophotographic process has been realized.
As a laser printer of this type, a printer adopting a multi-beam scanning system has recently been developed. In this printer, a plurality of beams are generated and a plurality of lines are scanned by these beams, thereby increasing a printing speed.
In such a laser printer, in order to generate a plurality of beams, a plurality of light sources (laser diodes) independently housed in different cases are used. In addition, in order to control each beam, a light amount monitoring element (photodiode) is used together with each laser diode. That is, a light amount of each laser beam is independently controlled in accordance with an output from each light amount monitoring element.
For this reason, in a conventional multi-beam scanning laser printer, light amount controllers must be provided in a number corresponding to that of scanning beams. As a result, an overall arrangement of the apparatus is complicated, and the apparatus becomes expensive.